EP2297083A2

EP2297083A2 - Citric acid ester mixtures and use thereof

Info

Publication number: EP2297083A2
Application number: EP09757374A
Authority: EP
Inventors: Michael Grass; Stefan Buchholz; Wilfried Büschken
Original assignee: Evonik Oxeno GmbH and Co KG
Current assignee: Evonik Operations GmbH
Priority date: 2008-06-03
Filing date: 2009-05-05
Publication date: 2011-03-23
Anticipated expiration: 2029-05-05
Also published as: DE102008002168A1; WO2009146991A2; US8431638B2; EP2297083B1; SA109300318B1; EP2857383A1; TWI461404B; WO2009146991A3; TW201004918A; US20110046283A1

Abstract

The present invention relates to mixtures of citric acid esters of the formula I, where R1, R2 and R3 each are aliphatic C5 or C9 groups, characterized in that the average chain length of the aliphatic groups in the mixture is in the range between greater than 5 and 7 and the average degree of branching of the aliphatic C9 groups is in the range between 0.9 and 2.2. The present invention also relates to the use of the citric acid ester mixture according to the invention as a plasticizer in plastic compositions. The present invention furthermore relates to a composition containing the citric acid ester mixture according to the invention in a mixture with additional components, containing plasticizers from the group of the alkyl esters of aromatic polycarboxylic acids, cyclohexane polycarboxylic acids, benzoic acid, or adipic acid, and to the use of such a plasticizer composition in plastic compositions, adhesives, sealing compounds, lacquers, paints, plastisols or inks. Plastic products produced from the plasticizers according to the invention can include profiled sections, seals, food packaging, films, toys, medical articles, sheet roofing, synthetic leather, floor coverings, underbody sealers, coated fabrics, wallpaper, cables and wire sheathings.

Description

Citric acid ester mixtures and their use

The present invention relates to mixtures of citric acid esters containing pentyl citrates, nonyl citrates and nonylpentyl citrates and to their preparation and their use as plasticisers for plastics.

Polyvinyl chloride (PVC) is one of the most economically important polymers. It finds many applications both as rigid PVC and as soft PVC.

To produce a flexible PVC, plasticizers are added to the PVC, with the majority of cases using phthalic acid esters, in particular di-2-ethylhexyl phthalate (DEHP), diisononyl phthalate (DINP) and diisodecyl phthalate (DIDP).

Due to discussions about reproductive toxicity, which in some cases have led to increased labeling and, in the case of toddler toys, also to restrictions on use, it must be assumed that the use of these phthalates will in future, especially in sensitive applications, such as food packaging and medical applications , will decline significantly. In addition, especially in applications for the interior, so for example in floor coverings, wallpapers and imitation leather, by various environmental associations a general substitution of phthalates is required. There is therefore a need for plasticizers which are not subject to labeling and which can be used as a substitute for DEHP but also DINP and which are produced from raw materials that are available in large quantities worldwide.

A conceivable alternative is the use of plasticizers based on citric acid, especially because it is accessible from renewable raw materials. It is known to use citric acid esters having three identical alkyl radicals, such as, for example, tri-n-butyl citrate or tri-2-ethylhexyl citrate (for example Gächter / Müller, Kunststoffadditive, 3rd Edition 1990, Carl Hanser-Verlag, pages 417-418). , In DE 10 2006 026 624 citric acid esters are based on primary C ₅ alcohols. Frequently, these esters are further dehvatized by acetylating the free hydroxyl group of the citric acid ester with a carboxylic acid or a carboxylic acid derivative, for example with the anhydride. The most well-known citric acid-based softener to date is acetyl tri-n-butyl citrate (ATBC), a substance that also has various approvals in sensitive applications.

Corresponding acylation processes are known, for example, from DE 1 099 523. From DE 35 20 750, such citric acid ester mixtures or mixtures of their acetyl derivatives with different alkyl radicals are also known, for example an ester mixture which has n-hexyl, n-octyl and n-decyl radicals.

Citric acid esters or mixtures of citric acid esters, which are used as plasticizers, are said to meet several requirements: their volatility must be low, so that it is too low during processing

Softener losses and a low environmental impact comes. For example, the ATBC is not optimal here. The compatibility of the plasticizer with the softening plastic must be large enough so that a high amount of it can be incorporated into the plastic and it comes even after prolonged use to no significant exudation of the plasticizer from the plastic. They have to produce good processing properties in mixtures with the plastic. In particular, it must be ensured that sufficient suitability exists for the large field of application of plastisol processing. In the event that a certain plasticizer (for example DINP) is to be replaced with a citric acid ester, similar properties would be desirable since this minimizes the conversion effort in the formulations and the process parameters. The most important properties here are the plastisol viscosity, the gelation and the efficiency (amount of plasticizer to achieve a specific softness).

In addition, the citric acid esters or their mixtures should be able to be prepared from readily available and inexpensive substances. EP 1 256 566 describes a plasticizer which consists of a mixture of Th-n-butyl citrate, di-n-butyl-2-ethylhexyl citrate, n-butyl-di-2-ethylhexyl citrate and tri-2-ethylhexyl citrate. This plasticizer is characterized by low volatility and good compatibility with PVC. Other positive features are not disclosed.

In WO 2007/038489 citrate mixtures with two different alkyl radicals which differ by at least 4 C atoms are also disclosed as plasticizers. These citrate mixtures are said to have a relatively low volatility and good performance in plasticized PVC

Effect properties. In the example, a citrate mixture is prepared by esterification of citric acid with n-butanol and isononanol, which is subsequently acetylated. Thus, it is a mixture consisting of acetyl tri-n-butyl citrate, acetyl di-n-butyl isononyl citrate, acetyl n-butyl di-isononyl citrate and acetyl th isononyl citrate.

EP 1 063257 B1 claims citric acid ester mixtures as plasticizers for PVC, the alcohol component of which comprises a mixture of various alcohols having a chain length range of C ₅ to C ₁₂ . It is not apparent from whether the citric acid is esterified with two or more alcohols, whether the alcohols have the same or different number of carbon atoms and whether they are primary, secondary, tertiary alcohols or mixtures thereof. In Example 1, a citric acid ester mixture is prepared by reacting citric acid with alcohols having a chain length range of Cβ to C10. This statement is ambiguous. Alcohols with one

Chain length of Cβ to C10 may mean that alcohols each having 6, 7, 8, 9 and 10 C atoms are present, but it may also mean two or more isomeric alcohols or two or more alcohols having different C number or isomeric alcohols together with alcohols of different C number. Furthermore, the molar ratio of the alcohols to each other and the type of alcohols (primary, secondary, tertiary) is not specified. In other words, any number of citrate ester mixtures with different properties are possible. No defined citrate ester mixture is assigned a property profile. Since the known citric acid esters and their mixtures do not correspond in all respects to the desired profile of requirements, the object was based on citric acid to develop a plasticizer with improved properties.

This plasticizer should be able to replace the previous standard plasticizer DINP with the least possible effort. In addition, the plasticizer should not contain any components as defined by the Committee for the Health Assessment of Construction Products (AGBB, for example, under https://www.worldwide.org) as SVOC components

(low volatility organic compounds) with a retention range on a non-polar gas chromatography column between Ciβ and C22, to classify (see Example 7). For some years now, stricter regulations for the approval of construction products in lounges have been adopted in Europe. Common to all national standards is the determination of a maximum level of emitted VOC after a period of storage in an emission test chamber. Only in Germany are there additional strict limits for low-volatility compounds (SVOCs). The lack of these compounds leaves the processor more freedom in the formulation. Thus, these esters of the invention can be used for the manufacture of articles for the interior. Furthermore, the volatility of the citric acid ester mixtures according to the invention is lower than that of butyl / 2-ethylhexyl, butyl / isononyl and butyl / isodecyl citrates with the same average chain length of the alkyl groups (see Example 6). In particular, for cost reasons, the hydroxyl group should not be acylated.

It has surprisingly been found that mixtures of citric acid esters whose hydroxyl group is not acetylated, the alkyl radicals attached to the oxygen of the carboxyl group are exclusively C ₅ or Cg radicals and whose average chain length is in the range between greater than 5 and 7, wherein the average degree of branching of the aliphatic Cg residues in the range between 0.9 and 2.2, meet the desired requirements. The subject of the present invention are mixtures of citric acid esters of the formula I

In which R ¹ , R ² and R ^{3 are} each aliphatic C ₅ or Cg radicals, characterized in that in the mixture the average chain length of the aliphatic radicals in the range between greater than 5 and 7 and the average degree of branching of the aliphatic Cg radicals in Range is between 0.9 and 2.2.

These mixtures of citric acid esters include the respectively mixed based on the aliphatic C ₅ - and Cg alcohols mixed citric acid esters, such as. As a dinonyl pentyl citrate, with a.

Likewise an object of the present invention is the use of the citric acid ester mixture according to the invention as plasticizer in plastic compositions.

The present invention also provides a composition comprising the citric acid ester mixture according to the invention mixed with further components comprising plasticizers from the group of the alkyl esters of aromatic polycarboxylic acids, cyclohexane polycarboxylic acids, benzoic acid or adipic acid and the use of such a plasticizer composition in plastic compositions, adhesives, Sealants, paints, paints, plastisols or inks. Plastic products made from the plasticizers of the present invention may be, for example, profiles, gaskets, food packaging, films, toys, medical articles, roofing membranes, artificial leather, floor coverings, underbody protection, coated fabrics, wallpapers, cables and wire sheathings.

The ester mixtures according to the invention have high compatibility with plastics and have good performance properties. In a lo special embodiment, the inventive

Citric acid ester blends able to replace the currently most important softener DINP in Europe without major recipe changes, as the main characteristics:

^■ Plastisol viscosities, i5 ^■ Gelation and

^■ softening effect are almost identical (see examples 3, 4 and 5). In addition, in plastisols, the increase in viscosities over time (aging) is significantly lower than with other citrates.

20

For the characterization of the citric acid ester mixture of the general formula I.

I 25 is the average chain length or the average number of C atoms of the aliphatic C ₅ or Cg radicals R ¹ , R ² and R ³ bound to the oxygen of the carboxylate groups. In the present invention, the average number of C atoms Cd of the alkyl radicals R ¹ , R ² and R ³ bonded to the oxygen of the carboxylate group is in the range of greater than 5 to 7, in particular in the range of 5.5 to 6.8.

In the case of a mixed citric acid ester of 2 alcohols with a moles of an alcohol with x C atoms and b moles of an alcohol with y C atoms, the average chain length is calculated as the average number of carbon atoms Cd of the alkylene side chain according to:

^■ Cd = (a ^* x + b ^* y) / (a + b)

If ni is the amount of C ₅ radicals in a given amount of the citric acid ester and n _{2 is} the corresponding amount of Cg radicals in the same amount, the average number of C atoms Cd is calculated as follows:

^■ Cd = (5 ni + 9 U ₂ ) I (ni + n ₂ )

With v = ni / n ₂ for the ratio of the amounts of C ₅ radicals to Cg radicals, the average chain length of the alkyl radicals or Cd is as follows:

^■ C _d = (5V + 9) / (v + 1)

If, for example, C ₅ radicals and Cg radicals are present in equimolar amounts, an average chain length of the alkyl radicals or a value for Cd of 7 is calculated.

According to the invention, the C ₅ radicals can have the following structures: n-pentyl (-CH ₂ -CH ₂ -CH ₂ -CH ₂ -CH ₃ ) 2-methylbutyl (-CH ₂ -CH (CH ₃ ) -CH ₂ -CH ₃ ) 3-methylbutyl (- CH ₂ -CH ₂ -CH (CHs) _-CH3) 2, 2-dimethylpropyl (-CH ₂ -C (CH ₂ ) ₂ -CH ₃ )

The citric acid ester mixtures according to the invention preferably contain n-pentyl and / or 3-methylbutyl radicals. In particular, the proportion of the sum of n-pentyl and 3-methylbutyl radicals in the entirety of the pentyl radicals is greater than 90%, very particularly greater than 95%. The proportion of 2,2-dimethylpropyl radical is preferably less than 2%, very particularly preferably less than 1%. The content of 3-methylbutanol on the entirety of the pentyl radicals is particularly preferably greater than 70%, in particular greater than 80%, very particularly preferably greater than 90%.

The Cg-radicals (-CH ₂ -CsHi ₇₎ in the inventive Estergemisch may also have different structures, wherein the group -CsHi branches ₇ of the Cg-radical is linear, simple, may be two or more times branched. Preferably, the ester mixture contains a plurality of isomeric Cg residues, the average degree of branching of which may preferably be between 0.9 and 2.2, and more preferably between 1.0 and 2.0. The determination of the average degree of branching of the Cg residues in the citric acid ester mixtures can be determined by ¹ H or ¹³ C NMR spectroscopic methods.

The citric acid ester mixtures I according to the invention can be prepared in the following ways: a) by esterification of citric acid, citric acid monohydrate or citric anhydride with pentanols and nonanols b) transesterification of citric acid esters, for example trimethyl citrate or thiethyl citrate, with pentanols and nonanols c) transesterification of a citric acid pentayl ester or Mixture with a citric acid mononyl ester or mixture d) Mixture of the respectively mixed citric acid esters based on the aliphatic C ₅ and Cg alcohols used e) Mixture of trinonyl citrates with tripentyl citrates The mixture according to the invention is preferably prepared by route a). Another preferred method of preparation is the combination of route a) and b). The citric acid or one of its anhydrides is esterified with pentanol or a Pentanolgemisch to pentyl ester (s), with excess pentanol serves as entraining agent for water. The resulting triphenyl ester is then transesterified with the calculated amount of nonanol. Optionally, the composition of the citric acid ester mixtures can be changed by distillation.

In the esterification of citric acid or a citric acid hydrate with the corresponding alcohol or alcohol mixture, the alcohol component is used in stoichiometric excess. The alcohol component is reactant and entraining agent for the separation of the water of reaction and optionally introduced with the citric acid water. The stoichiometric excess is preferably 5 to 50%, in particular 10 to 40%, particularly preferably 15 to 35%.

The esterification is preferably carried out in the presence of an esterification catalyst. In principle, acids such as sulfuric acid, methanesulfonic acid or p-toluenesulfonic acid, other mineral acids or metals or their compounds can be used as catalysts. Suitable z. As tin, titanium, zirconium, which can be used as finely divided metals or expediently in the form of their salts, oxides or in the form of soluble organic compound. However, the metal catalysts are compared to the proton acids high-temperature catalysts, which often reach their full activity only at temperatures above 180 ⁰ C.

The catalyst concentration can be varied widely depending on the type of catalyst. Concentrations of 0.05 to 2% by mass, preferably of 0.1 to 1% by mass, particularly preferably of 0.15 to 0.5% by mass, are usual for protic acids. Although higher acid concentrations increase the reaction rate, they can promote side reactions. For example, the dehydration of citric acid or its partial ester or avoid Vollester, it is expedient, the esterification in a temperature range of 120 ⁰ C to 180 ⁰ C, preferably from 130 ⁰ C to 170 ⁰ C and most preferably at 155 ⁰ C to 165 ⁰ C to carry out.

The aliphatic Cg alcohols to be used are commercially available in various compositions on the market. In the context of this invention, it is also possible to use nonanol mixtures which, in addition to Cg, also contain amounts of Cs and Cio alcohols.

In the esterification is used as the Cg-Al kholkomponente preferably a Cg-alcohol mixture obtained by hydroformylation of a Cs olefin mixture, prepared by oligomerization of linear butenes after the Octol process on a nickel-containing catalyst, and subsequent hydrogenation.

The citric acid ester mixtures according to the invention can be used as plasticizers, in particular in plastic compositions, adhesives, sealants, paints, paints, plastisols, artificial leathers, floor coverings, underbody protection, coated fabrics, wallpapers or inks. The plasticizers according to the invention may preferably be used in profiles, seals,

Food packaging, films, toys, medical articles, roofing membranes, artificial leather, floor coverings, underbody protection, coated fabrics, wallpapers, cables and wire sheaths, particularly preferably be used in food packaging, toys, medical supplies, wallpaper and floor coverings.

In particular, compositions according to the invention which contain the citric acid ester mixture can be obtained using the citric acid ester mixtures according to the invention. Such compositions may comprise the citric acid ester mixture of the invention alone or in admixture with other plasticizers. If the compositions according to the invention the citric acid ester mixture according to the invention in admixture with others Have plasticizers, the other plasticizers may preferably from the group of dialkyl phthalates, preferably with 4 to 13 carbon atoms in the AI kyl chain; Trimellitic acid alkyl esters, preferably having 4 to 10 C atoms in the side chain; Dialkyl adipate and preferably terephthalic acid dialkyl ester each preferably having 4 to 10 C atoms in the side chain; 1, 2-Cyclohexandisäurealkylestern, 1, 3-Cyclohexandisäurealkylestern and 1, 4-Cyclohexandisäurealkylestern, preferably 1, 2-Cyclohexandisäurealkylestern, each preferably with alkyl = alkyl radical having 4 to 10 carbon atoms in the side chain; Dibenzoic acid esters of glycols, preferably with di- or ethylene glycol as well as di- or tripropylene glycol; Alkylsulfonsäurester of phenol preferably having an alkyl radical containing 8 to 22 carbon atoms; Polymer plasticizer, Glycehnester and Benzoesäurealkylester, preferably with 7 to 13 carbon atoms in the AI kyl chain, be selected. In all cases, the alkyl radicals may be linear or branched and the same or different. In addition to citric acid ester mixtures, the composition particularly preferably has a alkyl benzoate with alkyl = alkyl radical having 7 to 13 carbon atoms, preferably isononyl benzoate, monoethyl benzoate, isodecyl benzoate, propylheptyl benzoate or benzoic decyl ester. The proportion of citric acid ester mixtures according to the invention in the mixture with other plasticizers is preferably from 15 to 90%, particularly preferably from 20 to 80% and very particularly preferably from 30 to 70%, with the mass proportions of all plasticizers present adding up to 100%.

The said compositions of citric acid ester mixtures and other plasticizers may be used as a softening composition in plastic compositions, adhesives, sealants, lacquers, paints, plastisols or inks. Plastic products made from the softening compositions of the present invention may include, for example, profiles, gaskets, food packaging, films, toys, medical articles, roofing membranes, synthetic leather, floor coverings, underbody protection, coated fabrics, wallpapers, cables, and wire sheathings. Preferred are from this group Food packaging, toys, medical supplies, wallpapers, coated fabrics, artificial leather and floor coverings.

The compositions according to the invention containing a mixture of citric acid esters may comprise a polymer selected from polyvinyl chloride (PVC),

Polyvinylidene chloride (PVDC), polyacrylates, in particular polymethyl methacrylate (PMMA), polyalkyl methacrylate (PAMA), fluoropolymers, in particular polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl acetate (PVAc, polyvinyl alcohol (PVA), polyvinyl acetals, in particular polyvinyl butyral (PVB), polystyrene polymers, in particular polystyrene (PS), expandable polystyrene (EPS), acrylonitrile-styrene-acrylate (ASA), styrene-acrylonitrile (SAN), acrylonitrile-butadiene-styrene (ABS), styrene-maleic anhydride copolymer (SMA), styrene-methacrylic acid copolymer, Polyolefins, in particular polyethylene (PE) or polypropylene (PP), thermoplastic polyolefins (TPO), polyethylene-vinyl acetate (EVA), polycarbonates, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyoxymethylene (POM), polyamide (PA), polyethylene glycol ( PEG), polyurethane (PU), thermoplastic polyurethane (TPU), polysulfides (PSu), biopolymers, especially polylactic acid (PLA), polyhydroxyl butyric acid (PHB), poly hydroxylvaleric acid (PHV), polyester, starch, cellulose and cellulose derivatives, in particular nitrocellulose (NC), ethylcellulose (EC), cellulose acetate (CA), cellulose acetate / butyrate (CAB), rubber or silicones and mixtures or copolymers of said polymers or their monomeric units. The compositions according to the invention preferably comprise PVC or homopolymers or copolymers based on ethylene, propylene, butadiene, vinyl acetate, glycidyl acrylate, glycidyl methacrylate, methacrylates, acrylates, acrylates or methacrylates with alkyl radicals of branched or unbranched alcohols having one to ten carbon atoms bound to the oxygen atom of the ester group (n), styrene, acrylonitrile or cyclic olefins.

Preferably, the composition of the invention contains as a PVC type

Suspension, bulk, microsuspension or emulsion PVC. Based on 100 parts by mass of polymer, the compositions according to the invention preferably contain from 5 to 200, preferably from 10 to 150, parts by mass Plasticizers.

The compositions according to the invention may contain, in addition to the constituents mentioned, further constituents, in particular z. As further plasticizers, fillers, pigments, stabilizers, co-stabilizers such as epoxidized soybean oil, lubricants, propellants, kickers, antioxidants or biocides.

The said polymers having compositions can be used as plastic compositions, adhesives, sealants, paints, paints, plastisols, artificial leather, floor coverings, underbody protection, fabric coatings, wallpapers or inks or for their preparation. The compositions mentioned can be, in particular, profiles, gaskets, food packaging, films, toys, medical articles, roofing membranes, artificial leather, floor coverings, underbody protection, coated fabrics, wallpapers, cables and wire sheathings. The compositions are preferably food packaging, toys, medical articles, wallpapers and floor coverings.

The following examples are intended to illustrate the invention without limiting it thereto.

Examples

Example 1: Synthesis of Citric Acid Esters

According to the following procedure, respectively, citric acid monohydrate was esterified with the mixtures of a shorter-chain (A1) and a longer-chain alcohol (A2) listed in Table 1. The alcohol mixtures were prepared in advance and represent in each case based on the citric acid, an excess of 33%. 1050 g of citric acid 1 hydrate (5 mol) and initially 800 g of alcohol mixture according to Table 1 were placed in a 4 liter distillation flask. The flask contents and the esterification apparatus were first purged with nitrogen over a dip tube for 30 minutes. The stirrer was switched on at low speed and the batch slowly heated. From about 115 ⁰ C precipitated crystal water from the acid, which was removed via a water separator. At 145 ^° C., 3.15 g of sulfuric acid (0.3% by mass, based on the carboxylic acid) diluted in 50 ml of alcohol mixture were added dropwise via an attached dropping funnel, which was purged with nitrogen for about 5 minutes before addition. During the addition, the dropping funnel was blanketed with nitrogen.

After reaching the reaction temperature of 160 ⁰ C, the remaining amount of alcohol was added slowly. It was ensured that the temperature remained constant. The resulting water of reaction was removed regularly. Upon complete addition of the alcohol, reflux was maintained at constant temperature via addition of toluene. After 5-7 hours, the reaction was stopped because the acid number had dropped below 1 mg KOH / g. Thereafter, the batch was cooled while continuing the nitrogen flow. The reaction effluent was then transferred to a 4 L reaction flask equipped with paddle stirrer, dip tube with attached

Dropping funnel and thermometer on a Claisen bridge, transferred. Here, too, care was taken that the inert gas atmosphere remained. It was then purged with nitrogen for a further 15 minutes, then vacuum was applied and after 15 minutes the heating was switched on. Under vacuum at 160 ⁰ C, the added toluene and the excess of alcohol were distilled off and then determined from the residue, the acid number according to DIN EN ISO 2114 and neutralized with ten times the stoichiometric amount of sodium hydroxide (5% by mass in water). For this purpose, the amount of leach was slowly added dropwise at 80 ⁰ C under atmospheric pressure, via the dropping funnel. After complete addition, the mixture was stirred at 80 ^° C. for 30 minutes. Thereafter, the stirrer was turned off. After a settling time of 30 minutes, the aqueous phase was drained off. In the crude ester then 5% aqueous sodium chloride solution was added (25% by mass based on the reactor contents) and it was stirred at 80 ⁰ C for 15 minutes. Thereafter, the stirrer was turned off. After a settling time of 30 minutes, the aqueous phase was drained off.

The neutralized ester 2% activated carbon (CAP Super, Norit), based on the reactor contents were added, the reactor evacuated and heated to 140 ⁰ C. Nitrogen was introduced into the product via a dip tube. The nitrogen was adjusted to 40 mbar by nitrogen flow and stripped for 30 minutes.

Subsequently, the apparatus was cooled to 80 ⁰ C.

The filter was filtered through a suction bottle with suction filter, whereby the suction filter was covered with filter paper on which a filter cake of filter aid was previously pre-pressed.

The purity of the esters thus prepared was then determined by gas chromatography. It was above 99.7% in all cases.

Table 1 :

Example 2: Production of plastisols

The weights of the components used for the different plastisols are shown in Table 2 below.

Table 2: Recipes [All data in phr (= parts by mass per 100 parts by mass of PVC)]

The plasticizers were tempered before the addition to 25 ⁰ C. First, the liquid ingredients and then the powdered ones were weighed into a PE beaker. By hand, the mixture was stirred with an ointment spatula so that no unwetted powder was present. The mixing cup was then clamped in the clamping device of a dissolver stirrer. Before immersing the stirrer in the mixture, the speed was set to 1800 rpm. After switching on the stirrer was stirred until the temperature on the digital display of the temperature sensor 30.0 ⁰ C reached. This ensured that the homogenization of the plastisol was achieved with a defined energy input. Thereafter, the plastisol was immediately heated to 25.0 ⁰ C. Example 3: Measurement of Plastisol Viscosity

The measurement of the viscosities of the plastisols prepared in Example 2 were carried out with a Rheometer Physica DSR 4000 (Paar-Physica), which is controlled by the associated US 200 software, as follows.

The plastisol was again stirred in the storage container with a spatula and measured in the measuring system Z3 (DIN 25 mm) according to the operating instructions. The measurement was carried out automatically at 25 ^° C. via the above-mentioned software. The following points were addressed:

A shear of 100 s ^"1 for the period of 60 s at which no measured values were recorded.

A downward ramp, starting at 200 s ^"1 down to 0.1 s ^{" 1} , divided into a logarithmic series with 30 steps each with a measuring point duration of 5 s.

The preparation of the measured data was carried out automatically by the software after the measurement. The viscosity was shown as a function of the shear rate. The measurements were carried out in each case after 2 h, 24 h and 7 days. Between these times, the paste was stored at 25 ⁰ C.

In the following Table 3, the respective viscosity values obtained after the indicated storage times are given by way of example for the shear rate of 100 s ^-1 . Table 3: Plastisol viscosities at a shear rate of 100 s ^"

Conclusion: The plastisols from the two citric acid ester niches according to the invention show practically the same viscosities as those with DINP. The three citrate comparisons plastisols (plastisols 4 - 6) are somewhat lower overall in level and also show a significantly higher viscosity increase with time. In particular, the latter means a higher workload for the processor. For this reason too, the plastisols according to the invention are to be preferred.

Example 4: Measurement of the gelling speed

The investigation of the gelling behavior of the plastisols was carried out in a Bohlin CVO oscillation viscometer (measuring system PP20), which was operated under shear stress control.

The following parameters have been set: Mode: Temperature gradient

Start temperature: 25 ⁰ C End temperature: 180 ⁰ C Heating / cooling rate: 2 ° C / min

Temperature after the measurement: 25 ^° C.

Oscillation frequency: 2 Hz

Delay time: 1 s Waiting time: 15 s

Continuous oscillation: on

Automatic shear stress specification: on

Starting shear stress: 0.3 Pa

Nominal deformation: 0.002 Gap width 0.5 mm

Carrying out the measurement:

On the lower measuring system plate, a drop of the plastisol formulation to be measured was applied with the spatula free of air bubbles. Care was taken to ensure that, after moving the measuring system, some plastisol could evenly escape from the measuring system (no more than approx. 6 mm around). Then the protective cover, which also serves for thermal insulation, was laid on and the measurement started.

The so-called complex viscosity of the plastisol was determined as a function of the temperature. Onset of gelling was evident in a sudden sharp increase in complex viscosity. The earlier this increase in viscosity began, the better the gelling ability of the system. For comparison, the temperature was determined from the curves by interpolation for each plastisol at which a complex viscosity of 1000 Pa * s was reached.

This resulted in the values listed in Table 4:

Table 4: Gelling behavior

The two citric acid ester mixtures according to the invention (in the plastisols 2 and 3) show in their respective formulations very similar gelling behavior as the DINP.

Example 5: Measurement of the Shore Hardness of Castings

The Shore A hardness is a measure of the softness of a test specimen. The further a standardized needle can penetrate into the sample body during a certain measuring period, the lower the measured value will be. The plasticizer with the highest efficiency gives the lowest value for the Shore hardness with the same amount of plasticizer. Conversely, with very efficient plasticizers, a certain proportion of the formulation can be saved, which in many cases means lower costs for the processor.

To determine the Shore hardnesses, the plastisols prepared according to Example 2 were poured into circular molds with a diameter of 50 mm. (50% RH 23 ⁰ C) then stored, the plastisols were gelled in the molds in a circulating air oven for 10 minutes at 200 ⁰ C, removed after cooling and prior to the measurement at least 16 hours under standard conditions. The thickness of the discs was about 8 mm.

The measurements themselves were carried out in accordance with DIN 53 505 using a Shore A measuring device from Zwick-Roell, the measured value being read off in each case after 3 seconds. Three different measurements were taken on each specimen at different locations (not in the marginal area) and the average was recorded in each case. Table 5 shows the results obtained. Table 5: Shore hardening

The citric acid ester mixture according to the invention (plastisol 2) has the same softening effect as DINP. It was thus possible to show that the citric acid ester mixtures according to the invention can replace the standard plasticizer DINP, in particular in the properties most important for plastisol processing, without changing the proportions of PVC and plasticizer.

Example 6 Determination of the Volatility of the Plasticizers by Thermogravimetry (TGA)

To obtain information on the volatility of the products, the citric acid esters prepared according to Example 1 were compared by means of the dynamic TGA method with respect to their mass losses at higher temperatures. For this purpose, about 40 mg of a sample were heated under a nitrogen atmosphere in a DuPont Instruments TGA 951 instrument in a temperature range of 20 to 300 ^° C. at a dynamic temperature increase of 10 K / min and the respective weight loss in% was determined. In Figure 1 the respective measuring curves are shown comparatively. The two citrates according to the invention show lower mass losses, especially at the higher temperatures. This is surprising due to the fact that the average chain length and thus also the average molecular weight are the same.

Example 7: Study for SVOC components

An SVOC is understood as meaning a substance which elutes on a nonpolar GC column between the retention times of C 16 and C 22 n paraffins.

For simplification, only the lowest boiling component of the respective citrate ester mixture was used in all cases, ie, th-3-methylbutyl citrate in cases 1 and 2 (according to Table 1) and tri-n-butyl citrate from comparative examples 3 to 5 (according to Table 1). examined.

This investigation was carried out by gas chromatography on a nonpolar column. The signal of the tributyl citrate appeared here immediately before the C ₂₂ paraffin signal, the signal of the Th-3-methylbutylcitrates clearly afterwards. Thus, tributyl citrate is considered to be SVOC and articles containing this plasticizer therefore run the risk of exceeding the maximum values, if any. Since tri-3-methylbutyl citrate is not considered to be SVOC according to this definition, there are no restrictions on the use of interior articles manufactured therefrom.

In summary, it can be said that the invention

Citrate ester mixtures could largely replace the previous standard plasticizer DINP without formulation adjustments and, in contrast to the comparison substances, have no components to be designated as SVOCs. In addition, in the case of the plastisols based on the citrate plasticizers according to the invention, the increase in viscosity over time is markedly lower, which results in a lower need for adjustment by the processor.

Claims

claims

1. mixtures of citric acid esters of the formula I,

In which R ¹ , R ² and R ^{3 are} each aliphatic C ₅ or Cg radicals, characterized in that in the mixture the average chain length of the aliphatic radicals in the range between greater than 5 and 7 and the average degree of branching lo of the aliphatic Cg- Residues range between 0.9 and 2.2.

2. mixtures of citric acid esters according to claim 1, characterized in that mixtures of mixed citric acid esters based on the i5 C ₅ - and Cg alcohols present side by side.

3. mixtures of citric acid esters according to claim 1, characterized in that mixtures of trinonyl and Tripentylcitraten present.

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4. Mixtures of citric acid esters according to claim 1, characterized in that the average chain length of the aliphatic radicals is in the range of 5.5 to 6.8.

25 5. mixtures of citric acid esters according to claim 1, characterized in that the C ₅ radicals consist of at least 90% of n-pentyl and 3-methylbutyl radicals.

6. mixtures of citric acid esters according to claim 1, characterized in that the C ₅ radicals consist of at least 70% of 3-methylbutyl radicals.

7. Mixtures of citric acid esters according to claim 1, characterized in that the average degree of branching of the Cg residues is between 1, 0 and 2.0.

8. Use of the mixtures according to claims 1 to 7 as plasticizers in plastic compositions.

9. Use of the mixtures according to claims 1 to 7 as a film-forming assistant in plastic compositions.

10. Softener compositions containing mixtures of citric acid esters according to claims 1 to 7.

11. Softener compositions according to claim 10, characterized in that they contain further plasticizers as mixture components from the group of alkyl esters containing aromatic polycarboxylic acids,

Cyclohexanepolycarboxylic acids, benzoic acid or adipic acid and Diolbenzoate from the group of diethylene glycols, dipropylene glycols, ethylene glycols or tripropylene glycols in a range of 15 to 90% by mass, with the mass proportions of all plasticizers used add up to 100% by mass.

12. Plastic compositions containing

Softening compositions according to claim 11.

13. Plastic compositions according to claim 12, characterized in that polyvinyl chloride (PVC) is contained.

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14. Plastic compositions according to claim 12, characterized in that polyalkyl methacrylate (PAMA) is contained.

15. Plastic compositions according to claim 12, characterized in that polyvinyl acetate (PVAc) is contained.

16. Plastic compositions according to claim 12, i5 characterized in that polyvinyl butyral (PVB) is included.

17. Plastic compositions according to claim 12, characterized in that

20 that polylactic acid (PLA) is included.

18. Plastic compositions according to claim 12, characterized in that polyhydroxybutyric acid (PHB) is contained.